While renovating a 300+ year old house, I had to insulate a small opening on the wall, that was previously there to act as a larder (cold pantry).

While choosing custom-made double glass panes on the internet, I saw that the price of shipping would be greater than the price of the glass itself, nearly tripling the total cost. That kept me wondering: couldn’t I make it somehow the same myself? Double glass is basically two glass panes separated by a small spacer. It shouldn’t be that complicated, right?

To start, we need to cut two panes in a glass. Mine was 6mm thick because I thought it would be more resistant to the outside agressions:

As in all insulating glass, the insulation is done by the air itself, immobile and trapped between the two glasses. This is done by using a spacer to keep the two glasses separated. Turns out that there’s actually some litterature out there regarding the optimal thickness of the spacers used.

I my case, I used an “old” paper from 1989: A study of pane spacing in glazing systems ¹, which reports the U-value of a glass depending on the thickness of the spacer:

As we can see, the U-value decreases with pane spacings up to 10mm, after which it starts to slowly get worse.

As I couldn’t manage to buy some spacer material (either Swisspacer’s, or something else), I just used some square cable conduit, which I found in 8mm thickness. It must then be filled with dessicant, so that the inside of the windows doesn’t start accumulating humidity and having water condensate²:

The spacers can then be glued to the first pane. However, before gluing the second one in, I filled the glass interior space with argon: first of all to evacuate the inside lingering humidity, but also because filling it with argon decreases the U-value by ~10%, which is good:

And we just have to glue the glass together through the spacers. The role of the first glue is not to be hermetic, but just to hold the glass itself. In my case I used super glue, which stick the panes really well to the conduit:

Once glued together, there is the delicate part of applying caulk to the whole side of the glass. Here, attention must be taken in order not to leave gaps, as humidity could come with the heating-cooling and thus thermal expansion-contraction of the inside air:

And basically, that’s how you DIY a double glazed window. Hope it lasts some years.. ;-)